FIG. 1 depicts a conventional magnetoresistive transducer 1 including a conventional magnetoresistive junction 10. For clarity, FIG. 1 is not drawn to scale. Magnetoresistive junctions 10, such as tunneling magnetoresistive (TMR) junctions, are used as read sensors in the conventional read transducer 1. Typically, conventional magnetoresistive junctions are formed by blanket depositing the layers for the conventional magnetoresistive junctions. This stack of layers typically includes layers for pinning layer 12 such as an antiferromagnetic (AFM) layer, a magnetic pinned layer 14, a nonmagnetic spacer layer 16, and a magnetic free layer 18. Other layers (not shown) might also be included in the magnetoresistive junction. For a conventional TMR junction 10, the nonmagnetic spacer layer 16 is a tunneling barrier layer. The barrier layer 16 is typically an insulator, for example aluminum oxide. After formation of the stack, a mask (not shown) is provided. The mask is typically a single layer photoresist mask with no undercut. The mask substantially covers the portion of the stack which is to become the conventional magnetoresistive junction 10. A remaining portion of the layers in the stack are then removed to define the conventional magnetoresistive junction 10. In such conventional methods, ion milling is the prevailing mechanism for defining the conventional magnetoresistive junction 10.
A single milling angle, φ1, is typically selected for defining the conventional magnetoresistive junction 10. This milling angle is typically at least five degrees and not more than thirty degrees from normal to the surface of the transducer. The single-angle milling proceeds until the stack has been completely milled through. Thus, the conventional magnetoresistive junction 10 is substantially defined. Because this single-angle ion milling often leads to redeposition of removed material on the sides of the conventional junction 10 and mask, a second, cleanup ion mill may be performed. This second ion mill is typically short in duration and performed at a high angle milling angle, φ2. For example, the angle is typically greater than sixty degrees from normal to the surface of the read transducer.
Although the conventional ion milling may define the conventional magnetoresistive junction 10, there are drawbacks. Ion milling may cause damage to the layers in a stack, particularly to oxide layers. Thus, the first, single-angle ion mill may damage the barrier layer 16 when the conventional magnetoresistive junction 10 is defined. This damage to the barrier layer 16 may adversely affect performance of the magnetoresistive junction 10. In addition, if the redeposition is not cleaned by the second ion milling, then metallic redeposition across the barrier layer 16 may result in shorting of the magnetoresistive junction 10. However, if the redeposition is cleaned, then the additional ion mill may further damage the barrier layer 16.
In addition, the damage due to ion milling may vary based on junction angle, θ, of the magnetoresistive junction 10 as well as on the milling angle, φ. The ion milling damage to the barrier layer 16 of the conventional magnetoresistive junction 10 occurs when the junction width is close to its final value. This is because portions of the stack damaged far from the final width of the conventional magnetoresistive junction 10 are removed during ion milling. As a result, ion milling damage is generally smaller for a shallow magnetoresistive junction (small junction angle θ and large milling angle φ) than for a steep magnetoresistive junction (large junction angle θ and small milling angle φ). This is because the shallow junction 10 is typically milled using a high milling angle φ1. As a result, the junction width for a shallow magnetoresistive junction 10 reaches its final value only when the single-angle milling comes towards its end. In contrast, for a larger junction angle θ formed using a small milling angle φ1, the width quickly gets close to its final value. As a result, the barrier layer 16 is exposed to more milling during the single-angle mill and experiences greater damage. Thus, a conventional magnetoresistive junction that has a steep (large) junction angle and/or which is formed using a small milling angle is more likely to be damaged during ion milling that defines the junction.
The conventional ion mill process may also create an undesirable junction profile. The single-angle ion mill or the single-angle ion mill in combination with the second ion mill may result in a kink 19, or step, at the barrier layer 16. This profile is due to the redeposition during the single-angle ion mill and different milling rates of the stack layers. For example, the barrier layer 16 typically mills at a different rate than the pinned layer 14 or free layer 18. Consequently, especially for a shallow junction angle, the kink 19 may occur. This junction profile with a kink 19 at the barrier layer 16 is undesirable because it adversely affects biasing of the magnetoresistive junction 10 by the hard bias structure (not shown). Consequently, performance of the read transducer 10 may be adversely affected.
Further, the trend in magnetic recording is to higher densities and, therefore, smaller junction widths. For example, current ultra-high density magnetic recording of approximately five hundred GB/in2 or more utilizes a TMR junction 10 having a width of not more than fifty nanometers. The junction width is desired not only to be small, but to have limited variations in order to maintain performance. Using the conventional single-angle ion milling, the junction width is primarily determined by the width of the mask used during ion milling. This is generally true whether or not the second ion mill is performed. At higher densities, the photolithography utilized to repeatably obtain a mask having a small width with limited variations may be difficult to achieve. Consequently, fabrication of the conventional magnetoresistive junction 10 may be more problematic.
There are conventional mechanisms for accounting for ion mill induced damage. Damage caused by the single angle ion mill that defines the junction and the second, cleanup ion mill may be repaired by an oxidation. However, such an oxidation may result in a relatively thick oxidation layer on the sides of the conventional magnetoresistive junction 10. Consequently, biasing of the magnetoresistive junction using a hard bias layer (not shown in FIG. 1) may be adversely affected.
Accordingly, what is needed is a system and method for providing an improved magnetoresistive junction.